Background. The National Adult Reading Test (NART) is widely used in research and clinical practice as an estimate of pre-morbid or prior ability. However, most of the evidence on the NART's validity as a measure of prior intellectual ability is based on concurrent administration of the NART and an IQ measure.
Method. We followed up 179 individuals who had taken an IQ test (the Moray House Test) at age 11 and administered the NART and the Mini-Mental State Examination (MMSE) at age 77. A subset (N=97) were also re-administered the original IQ test.
Results. The correlation between NART performance at age 77 and IQ age 11 was high and statistically significant (r=0·73; P<0·001). This correlation was comparable to the correlation between NART and current IQ, and childhood IQ and current IQ, despite the shared influences on the latter variable pairings. The NART had a significant correlation with the MMSE but this correlation fell to near zero (r=0·02) after partialling out the influence of childhood IQ.
Discussion. The pattern of results provides strong support for the claim that the NART primarily indexes prior (rather than current) intellectual ability.